Have a look at
http://zaurus.spy.org/ . Huge collection of links to websites will information on the Zaurus.
And a quick rundown of what Linux, the kernel and a ROM are...
Linux is an open-source (free) operating system created by Linus Torvalds in the early 1990s. It was originally a hobby, but is so much more than that now. It is very commonly used on network and internet servers because of it's security and stability over Windows, and is becoming more common on desktop and laptop computers. It is Unix based, like
almost every other major OS (Mac OS X, Solaris, <Free/Open/Net>BSD, etc.) except Windows. It is the operating system that the Zaurus runs on.
The kernel is the actual core of the operating system, and it's hard to explain what it does in simple terms. It is put on the Zaurus in the form of a compressed image, often flashed using a file called zImage or zImage.bin.
The ROM is the actual set of programs and utilities on the Zaurus. There are different versions (many for the 5500), that you can use and play around with, each with their own strengths and weaknesses.
As a note for you is you try out different ROMs, be sure that they are intended for the 5500, as other ROMs could damage it. The 5500 is also sometimes referred to as the "Collie".
